230 BO AD ENGINEERING
to traffic with an absence of vibration. It seems probable that
transverse joints, unless formed obliquely, may prove to be a source
of weakness, and perhaps the starting-point for setting up wariness.
Much will depend on the care with which the concrete is laid.
Earth Roads.
In hot, dry climates, where earth roads predominate, the surface
becomes corrugated almost immediately after blading. It is a
curious fact that a well-sprung car can travel over the wavy surface
better at high speeds than at low speeds; at 60 m.p.h. the wheels
seem to contact the tops of the waves only.